A Pokémon may have either one or two types: For instance, Charmander is a Fire type, while Bulbasaur is both a Grass type and a Poison type. With the current 18-type system, there are 324 possible ways to assign types to Pokémon, with 171 unique combinations. As of Generation VII, 146 different type combinations have been used. Similar to Pokémon, Pokéstar Studios opponents also have types.

A move has exactly one type. The type of a damaging move typically defines which types of Pokémon it is super effective against, which types of Pokémon it is not very effective against, and which types of Pokémon it is completely ineffective against.

If the type of a move is super effective against one of the opponent's types but not very effective against the other (such as Razor Leaf, a Grass-type move, used against a Gyarados, a Water/Flying Pokémon), then the move deals normal damage;

If the type of move is completely ineffective against one of the opponent's types, then the move does no damage, even if the opponent has a second type that would be vulnerable to it (as in Thunderbolt, an Electric-type move, used against a Quagsire, a Water/Ground Pokémon).

Status moves typically do not employ type effectiveness; however, Ground-type Pokémon are immune to Thunder Wave based on type interactions, and Ghost-type Pokémon are immune to Glare based on type interactions in Generation II and III only. Furthermore, status moves may be unable to affect Pokémon based on type-related interactions other than effectiveness; for example, Poison-type Pokémon cannot be afflicted with poison and are thus unaffected by Poison Gas.

Type chart

A type chart, also known as type matchup chart, shows which modifiers are applied to move types when attacking Pokémon of each type. If the defending Pokémon is dual-typed, the modifier is calculated as the product of the modifiers for both of its types: a Flying-type move would hit for 4× damage on a Bug/Grass Pokémon, while a Ground-type move used against the same would do only a quarter of the normal damage. (A complete ineffectiveness against either type will make the move deal no damage, since 0 multiplied by any number is 0.)

The type chart differs depending on the generation of games it is from. The current type chart is shown below.

Dual-type damage misinformation glitch

In Generation I only, if a damaging move is used on a Pokémon with two types such that one of its types is weak to the move and the other type resists the move, it will correctly receive neutral damage, but the incorrect message will be displayed on-screen. This does not occur in Pokémon Stadium.

When the type of a move matches one of the types of the Pokémon using it, the attack power will be increased by 50%. This is referred to as same-type attack bonus, or STAB for short. As an example, an Aron that knows the Steel-type move Metal Claw will have the move's power increased by 50% because one of Aron's types is Steel; the power of Cut would not be increased (because none of Aron's types is Normal).

??? type

The ??? type is the only type to have been removed from the core series games. The ??? type only existed from Generation II to Generation IV, and was primarily used in the core series as the type of the move Curse. It was removed in Generation V, and Curse became a Ghost-type move. Any damaging moves given the ??? type deal regular damage against all types, and any Pokémon given the ??? type takes regular damage against all moves.

Shadow

While not generally regarded as an actual type, in Pokémon XD, Shadow moves have their type listed as "------". Shadow Pokémon can be considered to be of this type, but they still retain their regular typing as well. In Pokémon XD, all Shadow moves are not very effective against Shadow Pokémon and super effective against non-Shadow Pokémon.

Typeless

There are situations where Pokémon or moves behave as if they were typeless, unable to receive STAB and boosts from type-enhancing items or Abilities. Typeless Pokémon take regular damage from all moves, and typeless moves deal regular damage against all Pokémon.

Glitch types

There are several types which only appear through the use of glitches, such as on the types of glitch Pokémon. Most famously this includes the Bird type, which was intentionally programmed into the code of the Generation I and II games but was not given to any real Pokémon. Other glitch types are the result of the game reading other data as if it were types. Like the ??? type, all glitch types have no special effectiveness (they both inflict normal damage against all types and take normal damage from all types).

In the Pokémon Ranger series

In the Pokémon Ranger series, each Pokémon has a group, equivalent to a type in the core series. The effectiveness of Poké Assists on wild Pokémon is dependent on the Pokémon's group.

In the Pokémon Rumble series

In the Pokémon Rumble series, the type effectiveness chart differs from the equivalent type chart in contemporaneous core series games. Moves that are ineffective in the core series deal 0.6× damage instead, moves that would be not very effective against one or both of the target's types deal ~0.8× or ~0.7× damage, respectively, and moves that would be super effective against one or both of the target's types deal ~1.2× and ~1.4× damage, respectively.

In Pokémon Battrio

Pokémon in Pokémon Battrio all have one type in line with one of their types in the core games. Battrio also includes two unique types exclusively for Arceus, the Full Plate and Eleven-Plate types.

Pokémon Battrio's type effectiveness chart is also unique, with different possible strengths for weaknesses or resistances. For example, while Grass-type Pokémon are weak to both Ice- and Fire-type moves, they are weaker to Fire-type moves than to Ice-type moves.

Players with a Memory Key can also gain experience towards different types that will level up their Type Levels, granting Pokémon of that type a bonus in Attack or HP.

In Pokémon Shuffle

Pokémon in Pokémon Shuffle each only have one type. Pokémon Shuffle's type effectiveness chart is also slightly different than the contemporaneous Generation VI chart, with 0× effectivenesses turned into ½× effectiveness.

In Pokémon GO

In the Pokémon GO, the type effectiveness chart differs from the equivalent type chart in contemporaneous core series games. Moves that are ineffective in the core series deal 0.51× damage instead (0.8× prior to June 21, 2017), not very effective moves deal 0.714× damage (0.8× prior to June 21, 2017), and super effective moves deal 1.4× damage (1.25× prior to June 21, 2017). If the defending Pokémon is dual-typed, the modifier is calculated as the product of the modifiers for both of its types.